1. Field of the Invention
The invention relates to aqueous organic dispersions which find particular utility as binders in the processing stages necessary for the production of ceramic articles. More particularly, the aqueous organic dispersions comprise polyethylene-acrylic acid copolymers dispersed in water for use as a binding agent for the formation of ceramics, particularly ceramic oxides such as aluminum oxides.
2. Description Or Prior Art
Ceramics are a material which enjoy use in applications which require materials which are durable and exhibit high heat resistance and low dielectric strength. Examples of uses of ceramics as engineering materials include include diverse applications such as uses as electrical insulators, to components within an aircraft jet turbine. Their success in such, and other applications, ensures that ceramics remain a viable engineering material for a multitude of present, and future developed applications.
As is known to the art, the formation of useful articles from a ceramic material requires that the ceramic be formed by some means to the desired shape and then subsequently treated to unify the individual particles of the ceramic into the final form of the article or part. Although many useful processes to achieve these ends exist, two particularly useful processes enjoying widespread use include molding and casting operations. In both of these processes, the ceramic material, such as alumina-oxide or silica-oxide are mixed or otherwise combined with a "binding agent" and then introduced into a form, mold, or die, so to impart a particular form upon the combined ceramic and the binding agent. The binding agent, also known to the art as a "binder" imparts a certain degree of dimensional stability and form retention to the mixture which is a necessary feature to a molding and casting operation. Frequently, after the removal of the mold, the formed mixture, or "preform" is removed and subjected to a heating operation, wherein the heat is used to drive off the binding agent leaving a molded part which is essentially free from any organic materials. Subsequent to this step, the preform may be subjected to a sintering operation.
Many materials which find successful use as a binder in such molding or casting operations are well known to the art. These binders consist primarily of organic materials, such as polymers, paraffin waxes, polystyrene, polyethylenes and other materials. Examples of such materials include polyolefin waxes, celluslosics, "agar" and acrylics.
While these have proven successful, the use of organic materials in binders is not without its disadvantages. It has been noted that the use of binders consisting essentially of organic components tend to require extended times during a "burn off" step, or the sintering operation in order to remove the organic materials from the preform. Further it has been observed that using binders consisting essentially of, or comprising a large amount of organic materials in its composition, tends to produce cracks and blemishes in the article being produced. It is believed that the generally higher boiling points of the organics necessitate longer times for the sintering step of the process, and that the exit of the organic from the preform structure is hindered due to the size of the organic molecules. This behavior is seen to induce the formation of the cracks and blemishes in the preform.
Therefore, it should be readily apparent that there remains a continuing need in the art for improved materials and improved methods which may be utilized in the formation of ceramic articles.